I have the Dinan strut bar (without the camber plates), and I'm running on 19's.

I do notice that the front end does seem appreciably tighter. The ride seems somewhat stiffer and more planted -- especially when cornering, on the twisties, and on entrance and exit ramps. I definitely notice a difference. Not a huge difference, but an appreciable difference.

I picked mine up (new) on eBay last year for approx. $375 (including s&h), and it was definitely worth it to me. At $600? Hard to say. Personally, I held off until I could get a better price.